The mechanisms whereby gonadal steroids influence the adult function and development of behavioral neuroeffectors are largely unknown. Our goals are to determine how androgenic steroids direct sexual differentiation of the nervous system so as to effect sexually dimorphic behaviors. The hypothesis is that androgen induces the masculinization of targets by gaining control of certain key developmental processes- proliferation, differentiation (neurite extension and synaptogenesis) and cell death. We propose to study the development of sex differences in the laryngeal motor neurons of the South African clawed frog, Xenopus laevis. Males display sexually differentiated vocal behaviors under strict androgen control. The muscles and motor neurons which effect calling are sexually dimorphic and hormone sensitive. The proposal aims to examine male/female differences in generation of vocal behaviors using physiological and anatomical techniques on adult and developing frogs. We will examine sex differences in generation of the vocal pattern, mate calling, by stimulating afferents to laryngeal motor neurons and recording activity on the laryngeal nerve. Laryngeal motor neurons of males are more numerous and have extensive dendritic processes; the connectivity of these cells also differs from larngeal motor neurons of females. We will study sex differences in responses of laryngeal motor neurons using intracellular recording; androgen affects on neuron activity will be assayed. The development of sex differences in vocal motor neurons will be examined anatomically and the time points when masculinization occurs identified. We will attempt to maculinize the behavior of females and the morphology of motor neurons by endocrine manipulation. The relative efficacy of direct versus indirect action by androgens on the masculinization of vocal motor neurons will be assessed by deafferentation and manipulation of muscle targets. Results of these studies will contribute to understanding the mechanism of action of steroids in the sexual differentiation of neuronal function. These findings will advance our knowledge of reproductive function, the development of gender identity and the mechanism of action of steroid drugs.